The invention relates to novel coating compositions prepared from a reactive polymer, a hydrazide compound and a silane compound. The coating compositions, which can be formaldehyde-free and isocyanate-free, cure to provide an interpenetrating network (IPN) coating having excellent properties.
Paints can be considered as falling into two general categories, namely, water-based paints and solvent-based paints. Which category of paint is suitable for a given application depends on the conditions to be experienced by the paint. Conventional water-based paints have generally been considered inferior to solvent-based paints with respect to weather resistance, solvent resistance and adhesion. Recently, however, the use of solvent-based paints has become environmentally disfavored, with an emphasis being placed on achieving acceptable results with paints having a relatively low volatile organic content (xe2x80x9cVOCxe2x80x9d). Specifically, efforts have been made to provide paints or coatings which are isocyanate-free and formaldehyde-free yet which exhibit acceptable physical characteristics.
It is therefore an object of the present invention to provide a coating composition which can be isocyanate-free and formaldehyde-free, yet exhibit good adhesion, durability, chemical resistance, water resistance and print resistance. This desired combination of properties has now been achieved by the novel coating compositions described herein.
The novel coating compositions described herein include a polymer, a hydrazide and a silane. The polymer has at least one reactive functional group. Non-limiting examples of the silane include silanes and polysilanes. Optionally, the coating composition includes a pigment. Coatings made from such compositions are also described. Methods of preparing a coating by applying the coating composition to a substrate and curing to form a film are also described herein. The invention also relates to a substrate coated with the novel coating composition.
The preferred coating compositions in accordance with this disclosure are formaldehyde-free and isocyanate-free, can be air cured and provide coatings that exhibit improved adhesion to the substrate, improved print and block resistance and improved solvent and water resistance.
Non limiting examples of the novel coating compositions in accordance with this disclosure include: (1) (a) a polymer, (b) a hydrazide and (c) a silane; and (2) (a) a polymer having at least one reactive functional group, the polymer also having a hydrazide group attached thereto, and (b) a silane.
Polymers useful in forming the coating compositions include, for example, acrylic polymers, modified acrylic polymers, polyepoxides, polyesters, polycarbonates, polyurethanes, polyamides, polyimides, polysiloxanes, polycarbamates and mixtures thereof. The molecular weight of the polymer is not critical. The polymer will generally have a molecular weight of 2,000 to 2,000,000 and preferably from 100,000 to 1,000,000.The polymer includes reactive functional groups. The functional groups can provide a site for attachment of the hydrazide-containing compound and also can provide a site for cross-linking by the silane compound as described in detail below. Suitable reactive functional groups include, for example, carboxyl, hydroxyl, epoxy, amino, alkylamino, multi-functional amine, amido, silane, silanol and keto groups or combinations thereof. The degree of substitution of the reactive functional groups is not critical, but rather can be adjusted to provide a coating having desired characteristics. Thus, for example, where carboxyl groups are present on the polymer, acid numbers as low as about 20 should provide adequate cross-linking to form a coating. However, if a coating which can withstand 200 MEK rubs is desired, an acid number in the range of about 40 to about 80 should be used. The polymer may be self-crosslinking or U.V. curable. It is within the purview of one skilled in the art to prepare suitable polymers containing reactive functional groups. Suitable polymers are commercially available from a variety of suppliers.
Where acrylic polymers are utilized, such polymers can be prepared from monomers such as acrylic acid and methacrylic acid, alkyl and cycloalkyl acrylates and methacrylates having 1 to 18, preferably 4 to 13, carbon atoms in the alkyl or cycloalkyl moiety, or mixtures of such monomers, by way of non-limiting example. Non-limiting examples of these include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate, isobutyl acrylate, tertiary butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, cyclohexyl methacrylate, and 2-ethylhexyl methacrylate.
The reactive functionality on the acrylic polymer may be incorporated by reacting functional monomers, such as those having carboxyl, hydroxyl, epoxy, amino, keto, silane, silanol, and alkylamino functional groups, by way of non-limiting example. Non-limiting examples of carboxyl containing monomers include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, 2-acryloxymethoxy-O-phthalic acid, 2-acryloxy-1-methylethoxy-O-hexahydrophthalic acid. Hydroxy functional monomers include 2-hydroxylethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxy butyl acrylate, hydroxybutyl methacrylate, allyl alcohol, and methallyl alcohol. A non-limiting example of an epoxy functional monomer includes glycidyl methacrylate. Non-limiting examples of alkylamino acrylates and methacrylates include aminomethyl, aminopropyl, aminobutyl and aminohexyl acrylates and methacrylates, dimethylaminoethyl acrylate, and dimethylaminoethyl methacrylate. Other suitable monomers include N-alkoxymethylacrylamide, and N-(butoxymethyl)acrylamide. Other ethylenically unsaturated monomers such as vinyl, styrene, xcex1-methyl styrene, vinyl toluene, t-butyl styrene may also be included to provide the desired physical characteristics. A non-limiting example of a keto containing monomer includes diacetone acrylamide. Non-limiting examples of silane containing monomers, include alkoxysilane functional monomers, such as gamma-methylacryloxy propyl-trimethoxy silane, gamma-methylacryloxypropyl-triethoxy silane, gamma-methylacryloxypropyl-triisopropoxy silane, etc. A silanol functionality is achieved upon hydrolysis of a silane functional monomer, such as those identified herein, by way of non-limiting example. Particularly useful polymers are carboxylated styrene acrylate polymers.
Modified acrylics can also be used as the acrylic polymer. Non-limiting examples of these include polyester-modified acrylics or polyurethane-modified acrylics, as are well known in the art. An example of one preferred polyester-modified acrylic is an acrylic polymer modified with xcex4-caprolactone. Such a polyester modified acrylic is described in U.S. Pat. No. 4,546,046 to Etxell et al. Polyurethane modified acrylics are well known in the art. An example is set forth in U.S. Pat. No. 4,584,354, the disclosure of which is hereby incorporated by reference.
Polyesters having hydroxyl groups, acid groups, or amino groups as reactive functional groups can also be used as the polymer in the present compositions. Such polyesters are well-known in the art, and may, for example, be prepared by the polyesterification of organic polycarboxylic acids (e.g., phthalic acid, hexahydrophthalic acid, adipic acid, maleic acid) or their anhydrides with organic polyols containing primary or secondary hydroxyl groups.
Polyurethanes useful as the polymer in the present compositions can be prepared, for example, by reacting polyisocyanate and polyol with an OH:NCO equivalent ratio of greater than 1:1, to obtain polyurethanes with terminal hydroxyl functionality. In this case, capping of the isocyanate occurs simultaneously with the synthesis of the polyurethane resin. Alternatively, polyurethane may be formed by reacting polyisocyanate and polyol with an OH:NCO ratio of less than 1:1. In this case, where excess isocyanate is used, the polyurethane having an unreacted isocyanate functionality is then reacted with a capping agent. Suitable capping agents include reactive alcohols or amines, by way of non-limiting example. Non-limiting examples of these are trimethylolpropane, ethanolamine, diethanolamine, Solketal, diols, triols, or a mixture of diols and triols. Preferably, any unreacted isocyanate is removed before using the polyurethane as the polymer.
Suitable carbamate functional polymers can, for example, be prepared from an acrylic monomer having a carbamate functionality in the ester portion of the monomer. Such monomers are well-known in the art and are described, for example in U.S. Pat. Nos. 3,479,328; 3,674,838; 4,126,747; 4,279,833; and 4,340,497, the disclosures of which are incorporated herein by reference. One method of synthesis involves reaction of a hydroxy ester with urea to form the carbamyloxy carboxylate (i.e., carbamate-modified acrylic). Another method of synthesis reacts an xcex1,xcex2-unsaturated acid ester with a hydroxy carbamate ester to form the carbamyloxy carboxylate. Yet another technique involves formation of a hydroxyalkyl carbamate by reacting a primary or secondary amine or diamine with a cyclic carbonate such as ethylene carbonate. The hydroxyl group on the hydroxylalkyl carbamate is then esterified by reaction with acrylic or methacrylic acid to form the monomer. Other methods of preparing carbamate-modified acrylic monomers can be utilized as well. The acrylic monomer can then be polymerized along with other ethylenically-unsaturated monomers, if desired, by techniques well-known in the art.
An alternative route for preparing a polymer useful in the present coating compositions is to react an already-formed polymer such as an acrylic polymer with another component to form a carbamate-functional group appended to the polymer backbone, as described in U.S. Pat. No. 4,758,632, the disclosure of which is incorporated herein by reference. One technique for preparing useful polymers involves thermally decomposing urea (to give off ammonia and HNCO) in the presence of a hydroxy-functional acrylic polymer to form a carbamate-functional acrylic polymer. Another technique involves reacting the hydroxyl group of a hydroxylalkyl carbamate with the isocyanate group of an isocyanate-functional acrylic or vinyl monomer to form the carbamate-functional acrylic. Isocyanate-functional acrylics are known in the art and are described, for example in U.S. Pat. No. 4,301,257, the disclosure of which is incorporated herein by reference. Isocyanate vinyl monomers are well-known in the art and include meta-isopropenyl-xcex1-xcex1-dimethylbenzyl isocyanate (m-TMI). Yet another technique is to react the cyclic carbonate group on a cyclic carbonate-functional acrylic with ammonia in order to form the carbamate-functional acrylic. Cyclic carbonate-functional acrylic polymers are known in the art and are described, for example, in U.S. Pat. No. 2,979,514, the disclosure of which is incorporated herein by reference. A more difficult, but feasible way of preparing the polymer would be to transesterify an acrylate polymer with a hydroxyalkyl carbamate. Other methods of preparing the polymer can also be used.
The polymer containing reactive functional groups is preferably provided in the form of a latex, with the term xe2x80x9clatexxe2x80x9d being used herein in a broad sense to designate any, generally aqueous dispersion of a water-insoluble polymer, the polymer being present in the form of particles.
Combined with the polymer and silane in the coating composition or grafted onto the polymer is a compound containing a hydrazide group. Preferably, the hydrazide group has the formula: 
wherein
R1 and R2 each independently represents H or substituted or unsubstituted alkyl.
The hydrazide group-containing compound can also comprise a hindered amine group as is often found in compounds known as hindered amine light stabilizer compounds (HALS). One example of such a compound has the formula: 
The hydrazide group-containing compound can also have the formula: 
wherein
R3 and R4 each independently represents H or substituted or unsubstituted alkyl, and
R5 represents substituted or unsubstituted alkyl, substituted or unsubstituted aryl, or 
wherein
L represents a divalent linking group, xe2x80x94NHxe2x80x94 or xe2x80x94Oxe2x80x94. The linking group is preferably aliphatic, but may also be aromatic, cycloaliphatic, or heterocyclic. Preferably, at least one of R3 or R4, and at least one of R6 and R7 represents hydrogen. In another preferred embodiment, all of R3, R4, R5, and R6 represent hydrogen.
The hydrazide group-containing compounds may be prepared from aliphatic organic acids, such as acetic acid, propionic acid, n-octanoic acid, adipic acid, oxalic acid, sebacic acid, and the like, by way of non-limiting example. The acid groups are typically reacted with hydrazine as is known in the art to produce the hydrazide derivative of the acid, although other methods can be used. A preferred hydrazide group-containing compound is adipic dihydrazide.
Non-limiting examples of other useful compounds comprising hydrazide groups include hydrazides of the formula Rxe2x80x94(CONHxe2x80x94NH2)n; bis-hydrazides of the formula NH2xe2x80x94NHxe2x80x94COxe2x80x94NHNH2; semicarbazides of the formula RNHxe2x80x94COxe2x80x94NHNH2; and thiohydrazides of the formula RNHxe2x80x94CSxe2x80x94NHNH2. In each of the above formulas for hydrazide group-containing compounds, n is a positive integer of at least 1. In a preferred embodiment n=2. R may be hydrogen (except for hydrazides or thiohydrazides when n is 1) or an organic radical. Useful organic radicals include aliphatic, cycloaliphatic, aromatic, or heterocyclic groups, preferably from 1 to 20 carbon atoms. The R groups should be free of substituents that are reactive with hydrazide groups.
Polyhydrazides (e.g., hydrazides or thiohydrazides where n=2) are preferably used to incorporate hydrazide groups onto the polymer by reacting one of the hydrazide groups with a hydrazide-reactive group on the polymer.
The polyhydrazide can be reacted onto the polymer, by reacting a polyhydrazide with an acrylic or polyester polymer having one or more anhydride or epoxy groups. Alternatively, hydrazine can be reacted directly with the reactive functional groups on the polymer (e.g., with acid groups on an acrylic polymer) to form a hydrazide-functional polymer. Conditions for reacting the hydrazide compound with the polymer are within the purview of one skilled in the art. Typically, the hydrazide compound is simply mixed into a dispersion containing the polymer. This may result in grafting of the hydrazine group onto the polymer. If desired, the hydrazide compound can be mixed with a solvent prior to addition to the polymer dispersion.
The amount of hydrazide compound added is not critical, but rather will depend on a number of factors including the degree of substitution of reactive functional groups on the polymer and the desired characteristics of the final coating. Typically, the hydrazide compound will be added in an amount of from about 0.25 to about 10% by weight, preferably about 0.5 to about 5.0% by weight, based on the weight of the total solids content of the coating composition. As those skilled in the art will appreciate, because in a dispersion the polymer will fold upon itself to form particles or micelles, the hydrazide compound will primarily react with reactive functional groups located on the outside of the particle or micelle. Thus, the reactive functional groups within the particle or micelle will remain available for crosslinking by the silane as the polymer molecular unfolds upon removal of water or other solvent from the coating composition. In particularly useful embodiments, a sufficient number of the reactive groups on the outside of the polymer particle or micelle are reacted with the hydrazide compound to prevent excessive gelling upon addition of silane. This will allow the coating composition to be prepared as a one package system.
To form the present coating compositions, a silane is included along with the hydrazide and polymer. By way of non-limiting example, the silane, hydrazide and polymer can be mixed together or the silane can be added to a combination of the hydrazide and the polymer. A non-limiting example of the formula of the silane is: 
wherein n=1 to 1000, preferably 1 to 100, most preferably 1 to 10; R is an optionally substituted hydrocarbon group containing from 1 to 20 carbon atoms (such as, for example, a methyl phenyl, alkyl or aryl group); R1 is the same or different at each occurrence and is a moiety selected from the group consisting of halogen, hydrogen, alkoxy, hydroxy, amino and epoxy groups; and R2 can be the same or different at each occurrence and is selected from the group consisting of R and R1 as defined above. The aminosilanes and epoxysilanes are particularly useful silanes for making the present coating compositions. Suitable silanes are commercially available from a variety of suppliers. Specific non-limiting examples of suitable silanes include:
allyltrimethoxysilane;
allyltrimethylsilane;
N-(2-aminoethyl)-3-aminopropyl-methyldimethoxysilane;
N-2-aminoethyl-3-aminopropyltrimethoxysilane;
3-aminopropylmethyldiethoxysilane;
3-aminopropyltriethoxysilane;
3-aminopropyltrimethoxysilane;
bis-(dimethylamino)dimethylsilane;
bis-(n-methylbenzamide)ethoxymethylsilane;
bis(trimethylsilyl)acetamide;
n-butyldimethylchlorosilane;
t-butyldimethylchlorosilane;
chloromethyltrimethylsilane;
3-chloropropyltriethoxysilane;
3-chloropropyltrimethoxysilane;
di-t-butoxydiacetoxysilane;
n,n-diethylaminotrimethylsilane;
dimethylchlorosilane;
dimethyldichlorosilane;
dimethyldiethoxysilane;
dimethylethoxysilane;
dimethylethoxysilane;
dimethyloctadecylchlorosilane;
diphenyldimethoxysilane;
1,3-divinyltetramethyldisilazne;
1,3-divinyltetramethyldisiloxane;
ethyltriacetoxysilane;
(3-glycidoxypropyl)methyldiethoxysilane;
(3-glycidoxylpropyl)trimethoxysilane;
hexamethyldisilane;
isobutyltrimethoxysilane;
3-mercaptopropylmethyldimethoxysilane;
3-mercaptopropyltrimethoxysilane;
3-mercaptopropyltriethoxysilane;
3-methacryloxypropyltrimethoxysilane;
3-methacryloxypropyltris(methylsiloxy)silane;
n-methylainopropyltrimethoxysilane;
methylcyclohexydichlorosilane;
methylcyclohexyldimethoxysilane;
methyltriacetoxysilane;
methyltrichlorosilane;
methyltriethoxysilane;
methyltrimethoxysilane;
n-methyl-n-trimethylsilyltrifluoroacetamide;
octadecyltrichlorosilane;
octyltrichlorosilane;
n-octyltriethoxysilane;
phenytriethoxysilane;
phenyltrimethoxysilane;
tetra-n-butoxysilane;
tetrachlorosilane;
tetraethoxysilane (teos);
tetrakis (2-ethoxyethoxy)silane;
tetrakis (2-methoxyethoxy)silane;
tetramethoxysilane;
tetrapropoxysilane;
trichlorosilane;
triethylchlorosilane;
triethylsilane;
trimethoxysilylpropyldiethylenetriamine;
n-trimethoxysilylpropyl-n,n,n-trimethyl ammonium chloride;
trimethylbromosilane;
trimethylchlorosilane;
trimethylsilylacetamide;
trimethylsilyliodide;
trimethylsilylnitrile;
trimethylsilyl trifluoromethanesulfonate;
vinyldimethylchlorosilane;
vinylmethyldichlorosilane;
vinylmethyldiethoxysilane;
vinyltrichlorosilane;
vinyltriethoxysilane;
vinyltriethoxysilane; and
vinyltris(2-methoxyethoxy)silane.
Another non-limiting example of the formula for the silane is:
Rxe2x80x94Sixe2x80x94(X)3 
wherein Rxe2x95x90(CH2)nY and n=0-3
X is a hydrolyzable group, usually an alkoxy group, capable of reacting with a polymer and/or silanol groups on the surface of a silicate or silica pigment
Y is an organofunctional group selected for reactivity with a given polymer.
Further, in the presence of water:
Rxe2x80x94Sixe2x80x94(X)3+H2Oxe2x86x92Rxe2x80x94Sixe2x80x94(OH)3+HX (usually an alcohol) 
Where:
Rxe2x80x94Sixe2x80x94(OH)3 can further react, such as: 
Where:
n1=xe2x89xa71
The amount of silane employed is not critical, but rather depends on a number of factors including the degree of substitution of reactive functional groups on the polymer and the desired characteristics of the final coating. As little as about 0.25% by weight based on the total weight of the solids content of the coating composition can be used to provide a coating. However, if a coating that can withstand 200 MEK rubs is desired silane amounts of from about 0.25% to about 10.0% by weight can be used.
Pigments are optionally included in the coating composition of the invention. Non-limiting examples of these pigments include silicas, such as colloidal silicas, mica, talcs, clays, aluminum silicates, chlorites, aluminum-magnesium silicates, magnesium silicates and china clay. It is advantageous in the present invention that the silane can be capable of co-crosslinking the polymer with the pigment(s). This results in an inorganic-organic crosslink when the silane is an organosilane, such as an organofunctional silane. In this case, the pigments are generally silica or silicate pigments. As a non-limiting example of this aspect of the invention, the silane may be an organosilane treated pigment which may be obtained by pre-treating the pigment with organosilane or by its formation in situ during the preparation of the coating composition.
In order to form a cured coating, one or more of the polymers as described above is crosslinked utilizing a one-package system or a two-package system. In a one-package system the polymer is combined with the silane to form a stable paint system at storage temperatures. In a two-package system, the polymer and the silane are kept separate until just prior to or upon application of the composition. Advantageously, no external catalyst (such as an organotitanate or inorganic acid) is needed in curing preferred compositions in accordance with this disclosure.
The inventive coating compositions may be clear or opaque compositions or anything in between and are useful for, by way of non-limiting examples, basecoats, topcoats, primers, fillers, etc. The composition may be in the form of substantially solid powder, a dispersion, or in a substantially liquid state. Liquid coatings may be solvent borne or waterborne. The coatings may also include solvents, pigments, catalysts, hindered amine light stabilizers, ultraviolet light absorbers, rheology control additives, photoinitiators and other additives known to one skilled in the art.
Coating compositions of the invention can be coated on an article by any of a number of techniques well-known in the art. These include, for example, spray coating, dip coating, flow coating, roll coating, curtain coating, vacuum coating, and the like. Non-limiting examples of the type of article coated or to be coated by the coating composition include a substrate, such as wood, ferrous or non-ferrous metal, plastic and the like.
After an article is coated with one or more layers of the above-described coating compositions, the article may then be subjected to conditions so as to cure the coating composition layers. Non-limiting examples of these conditions include air drying or baking. Curing is achieved by removing water, such as the water of the reaction or the water in a water borne coating. Although air curing may advantageously be used with the coating compositions described herein, heat-curing is preferred. Generally, heat curing is effected by exposing the coated article to elevated temperatures. Curing temperatures will vary depending on the particular compounds employed on the composition, however they generally range between about 20xc2x0 C. and about 180xc2x0 C., and are preferably between about 50xc2x0 C. and about 120xc2x0 C. The curing time will vary depending on the particular components used, and physical parameters such as the thickness of the coating layers applied, however, typical curing times range from about 0.5 to about 30 minutes.
The present invention is illustrated by the following non-limiting example.